The game would play like a traditional beat em up for the most part. You have your regular enemies that punch and kick, and “special” enemies that try to fatten you up. The way weight gain works is that your stats will change and you become slower, stronger and tankier for every weight milestone you reach. But if you get too much weight, you become immobilized and lose a life. You can also gain weight in restaurants, but never to the point of immobility. It would also be possible to lose weight by going to a gym, running around, or by using certain items. As you progress, you level up and get items that affect the system in many ways, such as changing how much you gain with enemy attacks, how much speed do you have and how much is the speed penalty for weight levels, how many more milestones you can reach before being immobilized and so on.
I don’t have the skills, nor the time to make this a reality. Heck i think this might be too ambitious of a scope for a game like this. Regardless, i wanted to leave this here, in case someone wants to do it.